Load diff stats for async diffs

What does this MR do and why?

In !83749 (merged) we added the ability to display diff stats in the commit view.

This MR ensures that diff stats are also displayed when the async_commit_diff_files feature flag is enabled.

Screenshots or screen recordings

before	after

How to set up and validate locally

1. Enable the async_commit_diff_files feature flag
2. Make a change to the uploaded file
3. Navigate to Repository > Commits > Select the most recent commit
4. The diff stats should be displayed

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.